I. Field of Invention
This invention relates to microstrip transmission lines and microstrip transmission line devices operating in the microwave and millimeter wave regions of the frequency spectrum and more particularly to a microstrip high reverse loss isolator for use with such microstrip transmission lines and devices.
II. Description of the Prior Art
Isolators are essentially two port, non-reciprocal attenuation devices which are used in RF transmission line applications, such as in the millimeter wave region of the frequency spectrum, for example, to provide a low loss transmission of electromagnetic wave energy from the input port to the output port but only a very limited or attenuated transmission of energy from the output port to the input port. They are often used in both military and commercial radar and communication systems for signal source protection. For example, isolators may be used in radar or communication systems to prevent or limit unwanted high energy millimeter wave weapons signals or other high level unwanted millimeter wave signals from entering the system via the antenna. For these applications, the reverse loss characteristic of the isolator should be as high as possible to provide a maximum isolation for the protected radar or communications system. Since planar type circuitry using microstrip is widely used in millimeter wave frequency applications because it permits the design of equipment having extremely small size and low weight which is desirable for many items of military and commercial equipment, such as the aforementioned radar equipment, for example, it is important that a suitable isolator for use with such applications not only have a high reverse loss but also be capable of being used with microstrip circuitry. Finally, a suitable isolator satisfying the foregoing criteria should also be capable of being fabricated relatively easily and inexpensively and should readily lend itself to assembly by means of current automated assembly techniques.